Standard-of-care treatment for Glioblastoma Multiforme (GBM) is comprised of surgery and adjuvant chemoradiation. Chimeric Antigen Receptor (CAR) T cell therapy has demonstrated disease-modifying activity in GBM and holds great promise. Radiation, a standard-of-care treatment for GBM, has well-known immunomodulatory properties and may overcome the immunosuppressive tumor microenvironment (TME); however, radiation dose optimization and integration with CAR T cell therapy is not well defined. Murine immunocompetent models of GBM were treated with titrated doses of stereotactic radiosurgery (SRS) of 5, 10, and 20 Gray (Gy), and the TME was analyzed using Nanostring. A conditioning dose of 10 Gy was determined based on tumor growth kinetics and gene expression changes in the TME. We demonstrate that a conditioning dose of 10 Gy activates innate and adaptive immune cells in the TME. Mice treated with 10 Gy in combination with mCAR T cells demonstrated enhanced antitumor activity and superior memory responses to rechallenge with IL13Rα2-positive tumors. Furthermore, 10 Gy plus mCAR T cells also protected against IL13Rα2-negative tumors through a mechanism that was, in part, c-GAS-STING pathway-dependent. Together, these findings support combination conditioning with low-dose 10 Gy radiation in combination with mCAR T cells as a therapeutic strategy for GBM.

Background: Diffuse hemispheric glioma (DHG), H3 G34-mutant, is a highly aggressive and fatal pediatric brain tumor, with a median survival of only ∼18 months and no effective targeted therapies. While chimeric antigen receptor (CAR) T cell therapy has shown success in B-cell leukemia and promise in other pediatric central nervous system tumors, it has not yet been evaluated explicitly in preclinical or clinical models of DHG. B7-H3 (CD276), a tumor-associated antigen overexpressed in pediatric brain tumors, represents a promising target for immunotherapeutic intervention in DHG. Here, we present the first preclinical evaluation of B7-H3-directed CAR T cell therapy in DHG. Methods: We evaluated B7-H3 expression in specimens from DHG patients and patient-derived cell lines. Two B7-H3-targeted CAR constructs were generated and evaluated for antigen-specific activation, cytokine production, exhaustion, and cytotoxicity in vitro. Therapeutic efficacy was assessed in multiple orthotopic DHG xenograft models, followed by multiplex immunofluorescence and serum cytokine profiling. Results: B7-H3 was highly expressed in DHG tumors and cell lines, but at minimal levels in normal brain tissue. B7-H3 CAR T cells demonstrated potent, antigen-specific cytotoxicity against DHG cells, with negligible activity against B7-H3-knockout DHG cells. In vivo, the intratumoral administration of B7-H3 CAR T cells led to significant tumor regression and a substantial extension of survival in 3 DHG mouse models, with durable tumor eradication. Conclusion: This study provides preclinical evidence supporting B7-H3 CAR T cell therapy as a highly effective immunotherapeutic strategy for DHG. Our findings support B7-H3 as a compelling immunotherapeutic target for DHG, laying the groundwork for clinical translation.